Adolescence is the critical neurodevelopmental period that occurs prior to assuming adult roles and responsibilities. This vulnerable developmental period is often characterized by impulsive behaviors, and may include initiation and progression of cannabis use, leading to other drug use and negative outcomes by young adulthood. Cannabis-using adults (many of whom started use during adolescence) often have a clinically significant cannabis withdrawal syndrome. Given the different patterns and rapid escalation that often occurs with adolescent cannabis users, reasons exist to believe that adolescent cannabis use is unique and the developmental processes altered by cannabis use may be distinct and important in determining factors that influence intentional abstinence. These developmental differences may produce a cannabis withdrawal syndrome that is different from the adult counterpart, as well as differences in the relationship of cannabis withdrawal with level of cannabis use. Although cannabis-using adolescents are often impulsive, we do not know how impulsivity is related to abstinence outcomes (e.g., lapse to drug use, and withdrawal) in this vulnerable population. This exploratory study (R-21 funding mechanism) will characterize the cannabis withdrawal syndrome among regular adolescent users and determine how processes of impulsivity are related to cannabis use, withdrawal, and lapse to drug use during a period of intentional abstinence. Participants will be adolescents (12-17 years of age) with moderate or heavy levels of cannabis use. Participants will complete a multimodal assessment battery that includes laboratory behavioral measures of impulsivity;self-report questionnaires of drug withdrawal and craving, impulsivity, and affect;and comprehensive assessment of recent drug use. These measures will be collected at baseline entry into the study, and during a 21-day period of intentional abstinence (e.g., during a 7-day acute withdrawal period, followed by a 14-day extended abstinence period). Our primary aims are to: (1) characterize the acute cannabis withdrawal syndrome for both moderate and heavy users;(2) determine how cannabis use and trait impulsivity are related at baseline;and (3) determine whether trait impulsivity at baseline predicts lapse to drug use during acute withdrawal and extended-abstinence periods. Our secondary aim is to characterize how laboratory-measured impulsivity changes across the period of intentional abstinence, and to determine how these changes relate to abstinence outcomes. 7. Project Narrative Public Health Significance: This study will yield clinically relevant data regarding underlying mechanisms central to understanding how impulsivity and abstinence outcomes such as cannabis withdrawal and lapse to drug use occur in cannabis-using youth. Our findings will inform our future studies aimed at developing individualized treatment and prevention programs for substance-abusing youth.